1. Field of the Invention
The present invention relates to a projecting device, and more particularly, to a projecting device for displaying computer images.
2. Description of the Prior Art
Digital micro-mirror devices are often used as image modules in reflective projecting devices for generating images by reflection and for projecting images. However, the distances between incident light beams and reflected light beams in such projecting devices are often small. Therefore, in order to avoid unwanted interference between light beams, the projecting devices must be made very large.
Please refer to FIG. 1. FIG. 1 is a perspective view of a prior art reflective projecting device 10. The reflective projecting device 10 comprises a reflective image module 12 comprising a plurality of controllable reflective surfaces (not shown) for modulating an incident light beam 11 and generating an image-containing reflected light beam 13, a total reflecting prism 14 for preventing interference between the incident light beam 11 emitted to and the reflected light beam 13 reflected from the image module 12, an optical device 16 such as a dichromatic mirror or a dichromatic prism, and a projecting lens 18 for focusing the image-containing reflected light beam 13 and outputting the image.
The projecting device 10 uses the total reflecting prism 14 to prevent unwanted interference between the incident light beam 11 emitted to and the reflective light beam 13 reflected from the image module 12. A long post focal distance 19, i.e. a long distance between the image module 12 and projecting lens 18, is therefore required. Therefore, the projecting device 10 must be very large and complicated leading to increased manufacturing cost. The prism 14 shortens ray traces of the incident light beam 11 and the reflective light beam 13 but also refracts light which causes chromatic aberrations and deterioration of the image. Also, the prism 14 reflects undesired deviated light onto the projecting lens 18 which lowers image contrast. Finally, assembly requirements for the total reflecting prism 14 are rigid which increases complexity of the structure and cost of manufacturing.
It is therefore a primary objective of the present invention to provide a projecting device to solve the above mentioned problems.
In a preferred embodiment, the present invention provides a projecting device comprising:
a light source for generating an incident light beam;
a reflective image module comprising a plurality of controllable reflective surfaces for modulating the incident light beam and generating a reflected image-containing light beam;
a first lens set for concentrating the incident light beam;
a reflective mirror for reflecting the incident light beam from the light source onto the image module through the first lens set; and
a second lens set installed between the light source and the reflective mirror for shortening an optical path from the light source to the reflective mirror;
wherein the optical path of the incident light beam reflected from the image module intersects a plane formed by the optical paths of the incident light beam from the light source to the reflective mirror and from the reflective mirror to the image module at one point.
It is an advantage of the present invention that the lens sets and the reflective mirror of the projecting device are specially arranged to prevent light crossings and to shorten the optical path thereby reducing the overall size of the projecting device. Moreover, the projecting device does not use prisms and so there is no generation of chromatic aberrations and no deviation of light. This results in ease of installation and lower manufacturing costs.